Aspects of the invention can relate to an image display device using an electro-optic modulator.
A moving image can be displayed on a related art image display device using an electro-optic modulator having a hold-type display mode, such as a liquid crystal display panel (liquid crystal device), as a blurred tailed-image due to the characteristic of an electro-optic modulator of this type. This is a phenomenon that does not occur in a CRT (Cathode Ray Tube) display that outputs an image impulsively.
In order to prevent a display of such a blurred tailed-image, the related art device needs to be controlled so that it outputs an image impulsively in the same way as the CRT. For example, as are disclosed in cited documents specified below, there are methods by which lights to illuminate the electro-optic modulator (hereinafter, descriptions will be given using the liquid crystal display as an example) are irradiated to the surface of the liquid crystal device intermittently, and a method by which the liquid crystal display can be divided into plural regions along a scanning line in the horizontal direction and lights are scrolled region by region.
According to JP-A-9-325715, control can be performed in such a manner that lights from the light source are irradiated to the surface of the liquid crystal display for only a limited time within one field period. This can be regarded as the method by which lights from the light source are irradiated to the liquid crystal device intermittently. Specifically, according to the above technique, a shutter can be provided on an optical path from the light source lamp to the viewer by way of the liquid crystal device, and by controlling the numerical aperture of the shutter (a ratio of a time during which lights are allowed to pass through with respect to one field period), an image is controlled to be displayed to the viewer for only a limited time in each field. Herein, a measure to prevent a display of a blurred tailed-image is taken by controlling the shutter in this manner. Also, by setting the limited time for keeping the shutter open in the latter half of one field period, the display can be started when a response of the liquid crystal display has achieved a stable state.
On the other hand, the other four cited documents specified below can be regarded as the method by which band-like lights are scrolled on the surface of the liquid crystal display in the vertical direction. In particular, according to JP-A-2004-4463, a lens array wheel that causes lights from the light source to undergo cyclical deflection is provided, so that lights are scrolled cyclically on the liquid crystal device by means of the lens array wheel. In this document, too, by taking a slow response of the liquid crystal device into account, control is performed in such a manner that lighting timing of a block of interest is delayed by a specific time from the writing to this block. This document also discloses, as another embodiment, a method by which a scroll disc having a partial spiral transparent portion is provided instead of the lens array wheel, so that lights having passed through the spiral light-transmitting portion are scrolled on the liquid crystal device in association with rotations of the scroll disc.
According to JP-A-2001-235720, JP-A-2002-6815, and JP-A-11-202286, a discharge lamp, such as a fluorescent light tube, is provided for each of plural regions in the vertical direction of the liquid crystal device, and the respective discharge lamps are lit in sync with the writing timing to the liquid crystal device, thereby preventing a display of a blurred tailed-image. In these documents, too, by taking a slow response of the liquid crystal device into account, for a discharge lamp corresponding to a region in which image data is being written, lighting timing is delayed by a specific time from the writing to this region.
Meanwhile, luminance becomes insufficient when the techniques disclosed in the first through fifth cited documents, that is, the method by which lights to illuminate the liquid crystal display are irradiated intermittently to the surface of the liquid crystal device, and the method by which lights are scrolled on the liquid crystal device region by region, are adopted to control the device to output an image impulsively for preventing a display of a blurred tailed-image as described. This poses a problem that dynamism of a moving image is lost as contrast is reduced. This problem may be solved by increasing luminance of the backlight. However, when luminance of the backlight is increased, there arises another problem that the entire screen becomes whitish for an image of a scene where original luminance is low.
To solve this problem, for example, JP-A-2002-40390 discloses a technique by which the luminance level of a video signal is detected, and adaptive light modulation processing (lighting control on solid-state light sources and control of pixel values) is performed region by region depending on the detected maximum luminance level. Hence, in the case of a video having a high maximum luminance level, that is, a bright video, luminance is set high by extending an image display period. Conversely, in the case of a video having a low maximum luminance level, that is, a dark video, a less-blurred, sharp moving image is displayed by shortening the image display period.
The effect of preventing a display of a blurred tailed-image can be expected to a certain degree with any of the techniques disclosed above.
However, the first document has a problem as follows. That is, because lights from the light source are irradiated to the entire surface of the liquid crystal device for only a limited time by means of the shutter, and a time for keeping the shutter open is set to a specific time (for example, ½ or ¼ of one field) in the latter half of one field period, image data for one field period has to be written before the shutter opens, which means the image data has to be written at a high speed. In addition, because the shutter employing liquid crystal, such as polymer dispersed liquid crystal and ferroelectric liquid crystal, is used, a closing-opening response raises another problem.
Problems with the second document are as follows. That is, because the scroll irradiation is performed, it is necessary to provide a mechanism to rotate the lens array wheel or the scroll disc. This technique also needs rotation control at high accuracy to scroll lights on the liquid crystal device exactly at predetermined timing.
Problems with the third through fifth documents are as follows. That is, because a discharge lamp, such as a fluorescent light tube, is used as the backlight of the liquid crystal device, lighting ON/OFF operations cannot be performed instantaneously. Hence, fine-tuned lighting control cannot be performed, and it is difficult to perform lighting ON/OFF operations at highly accurate timing. Moreover, the discharge lamp has irregularities in luminance and color at start-up of lighting.
Meanwhile, as has been described, the sixth document performs adaptive light modulation processing, and the effect of playing back a less-blurred sharp moving image can be expected to a certain degree.
However, in order to improve the image quality of the image display device using the liquid crystal device, there are still many problems that cannot be solved by the techniques disclosed in the first through sixth documents. For example, when the liquid crystal device is illuminated region by region as described above, it is necessary to further enhance homogeneity of brightness across all the regions (the entire one screen) as well as homogeneity of brightness within each region.
In order to further enhance homogeneity of brightness across all the regions (the entire one screen) as well as homogeneity of brightness within each region, a technique of providing a diffusing plate or a rod integrator has been proposed in various manners. However, homogeneity of brightness across all the regions (the entire one screen) as well as homogeneity of brightness within each region cannot be enhanced satisfactorily by merely providing the diffusing plate or the rod integrator, and the need for further improvements has been increasing.